Not claiming any authority ( I have tinkered a good bit about my Rotax 912, especially the electrics, but never touched the US'an stuff) I think the T/S may have it right: if no electrical connections are made, nothing can go wrong. What can and will go wrong is to generate even the slightest bit of field (as suggested in the previous reply), that will unavoidably create output and that has to go somewhere. So I think one can be on the very very safe side of things by shortcircuiting both the field and the load connections of the alternator, either with a bit of (thick!) wire or, perhaps even more prudent, with a low resistance, a car bulb or so. But there ought to be no need for such extreme prudence. I think